1. Field of Invention
The present invention relates to a vascular implant that is implanted into an artery for repair or bypass of arterial injury. The vascular implant includes a stent-graft that is delivered intraluminally into an artery for repair of a vascular lesion and more specifically for repair of abdominal aortic aneurysm. The vascular implant further includes an attachment means that provides attachment of a stent-graft to a vessel wall.
2. Description of Prior Art
An abdominal aortic aneurysm is an outpouching of the wall of the aorta that can continue to expand over time possibly leading to rupture and mortality. The outpouched wall is generally filled with thrombus except for a generally tortuous pathway for blood flow through an opening in the thrombus. This thrombus can become organized over time as fibroblasts and other cell types infiltrate and form a more organized matrix material containing collagen and other tissue. Typically such aneurysms occur below or caudal to the renal arteries or veins and can extend distally into the right or left common iliac arteries or further distally into the right or left femoral arteries. The right renal vein which crosses over the ventral surface of the aorta can provide some support to the ventral surface of the aorta an help resist aortic distention. Aortic distention can occur very abruptly just distal to the renal vessels reaching a diameter of six centimeters or greater and causing the onset of accompanying symptoms and requiring repair. Generally the blood flow pathway through the thrombus does not follow these abrupt changes found in the vessel wall but rather continues on in a more direct albeit tortuous path through the thrombus found in the aneurysmal aorta. The abdominal aortic aneurysm can sometimes have a proximal neck or region where the aortic diameter appears to be of normal diameter. This proximal neck region is sometimes found just caudal to the renal vessels. The abdominal aortic aneurysm can sometimes also have a distal neck region located just proximal to the aorto-iliac bifurcation. In this minority of patients the abdominal aortic aneurysm does not extend to the iliac arteries or farther distally. Aortic distention in the majority of patients can extend into one or both of the iliac or femoral arteries; repair of this abdominal aortic aneurysm can involve treatment of the iliac and femoral arteries as well. The common iliac artery divides to form the external and internal iliac arteries. The internal iliac artery (also called the hypogastric artery) is important in providing a supply or blood to the pelvic region, genital organs, and other areas and is most often not aneurysmal. The external iliac artery is commonly involved in the aneurysm and extends distally along an oftentimes very tortuous path to form the common femoral artery.
Surgical repair of an abdominal aortic aneurysm is an extensive procedure associated with a high incidence of morbidity and mortality and requiring many days of hospital stay. Older patients are often not capable of withstanding the trauma associated with this surgery. Repair of abdominal aortic aneurysm intraluminally through access from the common femoral artery can provide the patient with an alternate method of treatment for abdominal aortic aneurysm without the accompanying surgical trauma and long hospital stay. Placement of an intraluminal stent-graft can be performed by an interventionalist using a minimal surgical cutdown to an ipsilateral common femoral artery for access of the device to the arterial system of the body. Generally an additional access site is placed percutaneously in the contralateral common femoral artery. It is often preferred to place at least one more access site cranial to the abdominal aortic aneurysm generally through an axillary artery or other artery of the arm. Spiral computed tomography, duel-plane angiography, intravascular ultrasound, magnetic resonance imaging, and fluoroscopy provide some of the diagnostic techniques used to determine the position, diameter, and length of the aneurysm such that an appropriate intraluminal prosthesis can be selected for intraluminal implantation. Placement of the intraluminal stent-graft requires that a leak tight seal be made between the stent-graft and the aorta and between the stent-graft and each of the iliac or femoral arteries if they are involved in the aneurysm. Failure to provide such a leak tight seal will allow blood flow at arterial pressure to access the space between the stent-graft and the outpouched aorta. Continued exposure to arterial blood pressure can result in further expansion of the aneurysmal sac and could lead to sac rupture. Several intraluminal stent-grafts have been described for use in treatment of abdominal aortic aneurysms.
Barone describes in U.S. Pat. No. 5,578,072 an apparatus for repairing an abdominal aortic aneurysm. He describes a one-piece bifurcated aortic graft having a balloon expandable stent at one end to secure main trunk of the stent-graft to the aorta caudal to the renal arteries. The one-piece aortic graft has additional expandable stents positioned at the end of each leg of the bifurcated graft to secure the stent-graft to the iliac arteries. This design requires that the length of the main trunk and length of each limb be established prior to implantation using the diagnostic techniques described earlier. Due to the tortuous nature of the blood flow pathway, it is impossible to properly size the length of the graft using these diagnostic techniques prior to implatation. If the stent-graft is sized too short, then a portion of the aneurysm may be left unprotected. If the stent-graft is sized too long for example, then the blood flow to one or both of the internal iliac arteries may be compromised. The method of securing the main trunk of the stent-graft to the aorta caudal to the renal arteries described by Barone is also inadequate in many situations. A balloon expandable stent placed caudal to the renal vessels will very often be located within thrombus and will not have the strength or stability of the aortic vessel wall to support the stent or the stent-graft from migration caudally. Barone teaches that a securing means that is expanded outwardly over an axial length will hold the cranial end of the main trunk in position near the renal vessels. Barone also does not describe any means to prevent the stent-graft from being kinked or crushed as it travels through the thrombus laden blood flow pathway within the aortic aneurysm. Forces imposed upon the stent-graft due to the surrounding thrombus or thrombus organization could easily cause the stent-graft of Barone to become kinked or stenotic thereby impairing its performance. Barone discusses the need to place a stent proximal to the renal arteries for the case that the abdominal aortic aneurysm extends through the aortic region containing the renal arteries. He does not provide a suitable stent-graft for treating infrarenal aortic aneurysm with abrupt wall distension just distal to the renal vessels.
Parodi describes in U.S. Pat. No. 5,591,229 stent-graft devices that are similar to those described by Barone in the above patent. Additionally, Parodi describes a stent-graft for treatment of an abdominal aortic aneurysm that does not extend into the iliac region. This straight tubular stent-graft has a balloon expandable stent positioned at its cranial end for placement into the proximal neck of the aorta distal to the renal vessels. A balloon expandable malleable wire is placed at the distal end of the stent-graft to provide contact of the stent-graft with the aortic wall in the distal neck of the aorta. This stent-graft has a similar problem associated with estimating the graft length due to the tortuosity associated with the blood flow pathway through the thrombus laden aortic aneurysm. The other problem sited with the device described by Barone are similarly shared by the Parodi device.
Chuter describes in U.S. Pat. No. 5,693,084 a one-piece bifurcated stent-graft for treatment of abdominal aortic aneurysm having self expanding springs positioned at the proximal end of the main body and at the distal ends of each limb of the graft. The springs expand radially upon release to conform the ends of the stent-graft to the lumen of the aorta. This stent-graft suffers the same problem described for Barone in determining the length of the stent-graft prior to implant. Further, the stent-graft material is not supported throughout the entire stent-graft length thereby providing ample opportunity for stent-graft kinking and deformation within the aneurysm. Chuter has positioned six barbs that extend outward from the self expanding spring on the proximal end of the stent-graft. Due to the geometry of the springs, the positioning of the barbs into aortic wall rather than into the thrombus contained within the aneurysmal wall is not very precise. This can lead to stent-graft migration after a period of time post implant. Other problems associated with the Barone device similarly apply to the Chuter device.
McDonald describes in U.S. Pat. No. 5,676,697 a two-piece component bifurcated intraluminal stent-graft for treatment of abdominal aortic aneurysm. The first stent-graft component is a flexible tubular member with a side cut near the middle of the tubular member that opens up via a self expanding stent to form a waist region that is seated in the aorto-iliac bifurcation region. Two legs of the first stent-graft component are seated into each iliac artery using stents attached to the distal end of each leg. A second stent-graft component is introduced through one leg of the first component and allowed to self expand in the main trunk of the aorta and form a seal with the waist of the first component. The proximal end of the second component extends proximally within the aorta and makes a seal as it expands outwardly against the flow lumen. This device would have difficulty with positioning the proximal end of the second component within the proximal neck of the aorta. Extreme tortuosity found in the flow lumen of the aortic aneurysm would not allow this device to conform to its shape and would not allow a tight seal to be formed between the proximal end of the second component and the aorta. Difficulty in determining the appropriate length for each of the two components would limit the usefulness of this device.
Glastra describes in U.S. Pat. No. 5,632,763 a bifurcated component stent-graft assembly for treatment of abdominal aortic aneurysm. The assembly consists of a base stent-graft that is introduced into the main trunk of the aorta from an intraluminal approach. The base stent-graft has a generally cylindrical shape with a conical region located at the distal end. Two secondary cylindrical stents are introduced through two branching arteries, one in each leg and are seated in the conical region of the base stent-graft. This assembly has several potential problems associated with it. Determining the appropriate length of the base stent-graft and each of the secondary stent-grafts cannot be accurately performed considering that all of the arteries involved can be very tortuous and difficult to estimate in length. The seal that is required at the junction of the main to the secondary stent-grafts may have a tendency for leakage due to the geometry of that junction. Glastra describes two cylindrically shaped secondary stent-grafts that are placed adjacent to each other and are required to expand out and seal against a larger cylindrical base stent-graft; this seal would be difficult to form and maintain. Glastra does not address specific means for attachment of the proximal end of the base stent-graft to the aorta.
Marcade describes in U.S. Pat. No. 5,683,449 a modular system for forming a bifurcated stent-graft for use in treating abdominal aortic aneurysm. The system includes a number of components that are delivered intraluminally to the site of the aneurysm and brought into contact with each other within the aneurysmal space. The primary graft member has a proximal stent at one end and has an decreasing diameter as the stent-graft extends towards its distal end. The base member has a Y-shaped structure with a proximal end that contacts the distal end of the primary graft member. The base member also forms two branches on its distal end, each branch being brought into contact with a tubular graft member that extends into an iliac artery. This modular system still requires that each individual component be sized for length and diameter in order to fit the vast differences found between abdominal aortic aneurysm patients. Each junction between individual components is also a site for potential leakage of blood into the space between the stent-graft and the native arterial conduit. Marcade shows approximately five barbs positioned on the proximal stent. Due to the geometry of the stent it is not possible to obtain precise positioning of the barbs into the aortic wall tissue to ensure long term anchoring that would prevent stent-graft migration and maintain an adequate leak tight seal.
Vorwerk describes in U.S. Pat. No. 5,562,724 describes a component bifurcated device for treating abdominal aortic aneurysm consisting of a main body and two tubular stent-grafts. The main body has an open proximal end and a distal bag-shaped end with two outlet openings formed in it. Two tubular stent-graft legs can be introduced through the iliac arteries of the patient and attached to the two outlet openings of the main body. Sizing the appropriate length of the main body in addition to the two stent-graft legs is difficult due to the tortuosity found in the blood flow pathway of the aorta and iliac arteries. Leakage at the attachment site of the stent-graft legs to the main body also is a major concern.
Palmaz describes in U.S. Pat. No. 5,683,453 and Marin in U.S. Pat. No. 5,507,769 two tubular stent-grafts that travel in parallel from the infrarenal aortic neck to each iliac artery. Each stent-graft has a stent positioned at each end of the tube to form a seal with the native artery. This system would also have difficulty in determining the appropriate length of the stent-graft due to vessel tortuosity. In addition, this system requires that the two proximal stents deform against each other and with the proximal neck of the aorta to form a leak tight seal; it is not likely that an appropriate seal or attachment to the proximal aortic neck would be made. Extending a plurality of stent tubular members further within the length of stent-graft create a stent-graft that is too stiff to pass through a tortuous iliac artery to reach the site of the abdominal aortic aneurysm.
Egoda describes in U.S. Pat. No. 5,591,228 a method of introducing a bifurcated stent-graft for abdominal aortic aneurysm treatment using three access points into the arterial vasculature. As with other intraluminal stent-graft procedures, two access sites involve the common femoral arteries. Egoda describes a third access site made in the left subclavian artery through which the stent-graft can be introduced. This method may allow better control over both ends of the stent-graft during implantation. The length of the stent-graft must still be determined prior to implant and estimation of the length of the blood flow pathway is difficult to determine using standard diagnostic equipment due to the tortuosity of the vessels involved in the aneurysmal dilation.
A one-piece endovascular graft is described by Piplani in U.S. Pat. No. 5,824,039 for treating a bifurcated abdominal aortic aneurysm lesion. This device has springs located at inlet and outlet ends to hold the graft in place. The springs also have barbs attached. The springs have a large zig zag appearance similar to other prior art attachment means and the barbs are not well protected from inappropriate snagging prior to deployment of the endovascular graft.
Modular intraluminal prosthesis are described by Lauterjung in U.S. Pat. No. 5,824,036 and by Fogarty in U.S. Pat. No. 5,824,037. Lauterjung describes a composite system using a magnetic tipped guidewire to assist in the assembly of the prosthesis and employs a stent at the ends of the prosthesis and elsewhere. Fogarty describes a self-expanding or resilient frame with a plastically deformable liner over the frame limiting the resilient expansion. Each of these two composite or modular systems shares similar problems to the composite systems described earlier, including the potential for leakage at the junction sites as well as leakage at the junction of the prosthesis with the vessel lumen.
The present vascular implant overcomes the disadvantages of prior art stent-grafts, attachment means, and vascular tubular members used for endoprosthetic aortic or arterial aneruysmal repair, or for arterial bypass or other arterial or venous reconstruction. The vascular tubular member of the present invention includes a vascular tubular member that can be intravascularly delivered to the site of vessel injury such as an aortic aneurysm where it is deployed in a manner that will exclude the vessel injury or aneurysm. This intravascular tubular member conveys blood flow from a proximal arterial region that is located proximal to an arterial lesion or aneurysm to one or more distal arterial vessels. One embodiment of the present invention is an intravascular tubular member having a folded tubular section that allows the length of the graft to be adjusted during the time of deployment of the intravascular tubular member. This intravascular tubular member allows the physician to deploy the exact correct length of tubular member for each individual patient and allows the intravascular tubular member to fit different patients that require intravascular tubular members of different lengths. The intravascular tubular member further can have a proximal attachment anchor positioned at its proximal end that allows the proximal end to be positioned accurately in the aortic wall tissue adjacent and distal to the renal arteries. The attachment anchor of the present invention is an attachment anchor that does not undergo significant length change during deployment thereby allowing the position of the attachment anchor within the aortic aneurysm to be accurately determined. The intravascular tubular member can also be anchored to the aorta proximal to the renal vessels for the condition that the aortic aneurysm is abruptly distended adjacent and distal to the renal arteries. The attachment anchor can include barbs to more firmly anchor the intravascular tubular member to the vessel wall. The intravascular tubular member can also include a distal attachment anchor to anchor the distal end of the intravascular tubular member to one or more distal vessels.
The structure of the vascular tubular member includes a woven structure formed from either multifilament polymeric strands or a composite of multifilament polymeric strands woven along with metal strands. This structure of the vascular tubular member wall is such that it can be supported in both the axial and circumferential directions with metal strands. The circumferentially oriented metal strands provide anti-kink and anti-crush characteristics to the vascular tubular member. The axially oriented metal strands can provide the vascular tubular member with axial compression resistance and ensure that the folded tubular section is maintained in a straight tubular form. These characteristics will provide the tubular sections of the present invention with a more stable pathway for the intravascular tubular member through the thrombus found within a typical abdominal aortic aneurysm. The one-piece construction of the intravascular tubular member of this invention does not allow for leakage at modular junctions such as that which can occur with prior art component or modular intravascular tubular member systems described earlier. One primary application for the intravascular tubular member of the present invention is in the treatment of abdominal aortic aneurysms. Although the description of the invention in this disclosure is directed toward treatment of abdominal aortic aneurysm, it is understood that the present invention is intended for treatment of other vascular lesions both arterial and venous including vessel bypass, traumatic injury, aneurysmal repair, and other lesions.
The intravascular tubular member of the present invention can be formed from a single straight tube having a proximal end and a distal end. As the intravascular tubular member is being inserted into the patient, it has a smaller nondeployed diameter and a shorter nondeployed length. After the intravascular tubular member is fully deployed, it has a larger deployed diameter and a longer deployed axial length. The straight intravascular folded tubular member is comprised of three sections, a proximal tubular section that includes a proximal tube with an open inlet end, a folded tubular section which includes a folded tube that is able to extend in axial length, and a distal tubular section that includes a distal tube with an open distal end. The proximal, folded, and distal sections are of a length that allows ease of insertion and implantation of the intravascular folded tubular member to vascular application. Alternately, the distal section can be very short and may only include the outlet end of the folded section. In the folded tubular section the folded tube is folded back and forth upon itself generating two circumferential fold lines and forming the folded tubular section of the intravascular folded tubular member. In the folded tubular section a portion of the outer surface of the intravascular folded tubular member is in direct contact with another portion of the outer surface, and a portion of the inner surface is in direct contact with another portion of the inner surface of the intravascular folded tubular member. The nondeployed axial length of the intravascular folded tubular member is shorter than the deployed axial length; the folded tubular section length will shorten as the deployed axial length of the intravascular folded tubular member gets longer. The folded tubular section is positioned distal to the proximal tubular section which can have a proximal attachment anchor attached at the proximal end. Distal to the folded tubular section is a distal tubular section that can have a distal attachment anchor attached at or near the distal end.
The intravascular folded tubular member can be delivered intraluminally by compressing the intravascular folded tubular member radially to form a compressed conformation that can be delivered to the abdominal aorta or other vessel through a sheath or other delivery means placed in a common femoral artery. Upon delivery of the intravascular folded tubular member into the aorta, the intravascular folded tubular member expands to its deployed diameter. For a self-expanding intravascular folded tubular member the deployed diameter is between the nondeployed diameter and an equilibrium diameter that the intravascular folded tubular member would attain if fully deployed without a restricting force applied from the vessel with which it is in contact. The deployed diameter is generally approximately equal to the diameter of the native vessel that is being repaired. The intravascular folded tubular member can also be expanded by a catheter containing a mechanical expansion means such as a balloon. A proximal attachment anchor can be deployed to form an attachment that seals the proximal end of the intravascular folded tubular member to the aortic wall adjacent and distal to the renal vessels. The proximal attachment anchor does not undergo a significant axial length change during its deployment and as a result can be placed accurately in a position adjacent to the renal vessels for a more reliable attachment to the aortic wall. This reduces any chance for distal migration of the intravascular folded tubular member over time. Attachment of the intravascular folded tubular member to the attachment anchor of the present invention occurs at significantly more sites than is found with other prior art abdominal aortic aneurysm intravascular folded tubular members with zig-zag wire attachment means. The increased number of attachment sites provides a better seal of the attachment anchor and the intravascular folded tubular member to the aortic wall. Barbs can be located on the attachment anchor of the present invention such that they are folded inward during insertion of the device and extend outwards upon deployment of the intravascular folded tubular member.
The distal end of the intravascular folded tubular member is then positioned at an appropriate location within the abdominal aorta, typically at the site of the distal aortic neck if such a neck exists. It is common to position the distal end of the intravascular folded tubular member into an iliac or femoral artery. As the distal end of the intravascular folded tubular member is being positioned, a portion of the folded tubular section will be unfolded allowing intravascular folded tubular member material contained within the folded tubular section to unfold thereby allowing the intravascular folded tubular member to lengthen to an appropriate deployed axial length that is required to isolate an aneurysm, bypass an artery, or repair in some other way an artery for that individual patient. The length of the tortuous blood flow pathway through the thrombus in the aortic aneurysm can be accurately and appropriately sized in situ when using the intravascular folded tubular member of this invention.
The material of construction for the wall of the vascular tubular member with a folded tubular section as described previously can be any material that is used in vascular grafts or a combination of materials used in vascular grafts and endovascular stents. Typical vascular graft materials include expanded polytetrafluoroethylene, polyester, silicone, carbon, polyurethanes, biological tissues, silk, composite materials, and others. Some of these materials can be formed into a tube through processing methods that include paste extrusion, electrostatic spinning, spinning without electrostatics, salt leaching, and others. Additionally, the vascular tubular member of this invention which includes the intravascular folded tubular member can be formed from fibers of the materials listed above that have been woven, braided, knitted, or formed into a tubular member. The fibers can preferably be formed of many filaments of a very small diameter and which are wound to form a multifilament fiber or strand Such a multifilament fiber can offer an enhanced sealing capability at the crossover points of a woven or braided fabric vascular tubular member material. It is therefore preferred that a woven or braided tubular member be formed with multifilament yarn or multifilament fibers to reduce blood leakage at crossover points of polymer strand with polymer strand or polymer strand with metallic strand. Typical materials used in the construction of endovascular grafts and stents include Nitinol, stainless steel, tantalum, titanium, platinum, and other metals, metal alloys, and other suitable materials of large elastic modulus. Strands of these and other materials can be interwoven or interbraided with the polymeric materials used in vascular grafts to form a composite wall structure of the present invention.
A tubular double weaving method can be applied to the construction of the wall of the present vascular tubular member. A construction that involves weaving both polymeric fiber and metallic strands in both longitudinal and circumferential directions can encounter crossover points of one metal strand with another. At such crossover points, leakage or seepage of blood can occur from inside the vascular tubular member to the space outside the vascular tubular member. To reduce or eliminate small pores at the crossover points a tubular double weave is preferred when a metal strand is woven on both the axial and circumferential directions. With this technique a metal strand in one direction is brought out of the surface or the plane of the weave at the crossover point. The woven polymeric material without the metal strand forms a continuous plane of weave beneath the crossover point with good sealing due to the multifilament strands. Thus, leakage cannot occur at metallic strand to metallic strand crossover points due to the elimination of the pores or leakage sites due to the double weaving.
The attachment anchor that can be positioned at the proximal and distal ends of the infravascular tubular member can be of the self-expanding design or it can require an internal force application to force it outward, such as that provided by a balloon expandable means. The attachment anchor can be used with an intravascular tubular member that has a folded tubular section or it can be used with any other tubular member found in the prior art or that is being used for intravascular treatment of vessel injury. The metal strands that can be interwoven or interbraided into the wall structure of the intravascular tubular member can preferably be of a spring nature such that they self expand from the compressed state to form the deployed diameter; the metal wires can also undergo a plastic deformation as the intravascular tubular member undergoes expansion from its compressed conformation to its deployed diameter upon exposure to forces imposed by a balloon catheter placed within its lumen.
One preferred embodiment the intravascular folded tubular member of the present invention is a one-piece bifurcated tubular structure or means that is used in the treatment of abdominal aortic aneurysm. The intravascular folded tubular member has a proximal tubular section with a single open inlet end and a bifurcated main trunk that provides passage into two proximal leg tubes. Each proximal leg tube is joined to a folded tubular section, and each folded tubular section is joined to a distal section. The proximal tubular section has a deployed diameter approximately equal to the diameter of the aorta at the aortic proximal neck immediately adjacent and distal to the renal vessels. The two proximal leg tubes can have a diameter approximately equal to the diameter of the iliac artery or femoral artery into which they are to extend. The proximal end of the main trunk can have an attachment anchor attached to provide accurate attachment of the open proximal end within the proximal neck of the aorta. The attachment anchor can include barbs or hooks that provide a more definite attachment of the intravascular folded tubular member to the wall of the aorta to prevent migration, provide a leak-tight seal, and help support the aorta from further distension at that location. The folded tubular sections each have two circumferential fold lines and are folded back and forth in a manner similar to that described earlier for the straight intravascular folded tubular member. Each folded tubular section has a portion of the outer surface of the intravascular folded tubular member in direct contact with a another portion of the outer surface, and it has a portion of the inner surface of the intravascular folded tubular member in direct contact with another portion of the inner surface. The folded tubular sections allow the bifurcated folded tubular member to assume a shorter nondeployed axial length during the delivery of the intravascular folded tubular member than its deployed axial length. Each folded tubular section is attached to a distal tubular section with an open distal end. The open distal end of each distal tubular section can have an attachment anchor attached to form a precise and leak-free attachment to the iliac or femoral arteries.
A preferred bifurcated intravascular tubular structure or member of the present invention consists of a proximal tubular section or means with a proximal attachment anchor attached to its inlet end, two folded tubular sections attached to the proximal tubular section, two distal tubular sections attached to the two folded tubular sections, and two distal attachment anchor attached to each open distal end. The bifurcated intravascular tubular means is generally introduced into the aneurysmal abdominal aorta intraluminally through a surgical cut down or percutaneous access made into one common femoral artery. A sheath or other introducing means provides suitable access for the intravascular folded tubular member into the blood flow pathway of the aorta. Attachment of the proximal attachment anchor to the aorta is generally made adjacent and distal to the renal vessels. This attachment anchor can be a self-expanding attachment anchor or a balloon expandable attachment anchor. The attachment anchor is preferably short in axial length, has minimal length change upon deployment to allow more accurate placement, and can have barbs extending outward upon deployment to provide better attachment of the intravascular folded tubular member to the vessel wall. The two distal sections of the bifurcated tubular means are generally positioned in the right and left iliac arteries, respectively. The distal ends of the two distal section along with the two distal attachment anchor are positioned at an appropriate location within the iliac or femoral arteries so as to properly exclude the abdominal aortic aneurysm and any additional iliac or femoral aneurysm. As these distal ends are being positioned, the two folded tubular sections will unfold an appropriate amount to allow the deployed axial length of the bifurcated tubular means to be precisely sized to the individual patient. Variations between patients can be accommodated with the folded tubular sections as well as inaccuracies between angiographic length estimations of the aortic aneurysm and the actual length of the aneurysm.
Distal attachment anchor which are attached to the distal ends of the distal tubular sections can be deployed to form a secure and leak-tight attachment to each iliac artery or femoral artery. The wall structure of the bifurcated folded tubular member is similar to that described for the single straight tube. A woven or braided composite of a polymeric multifilament fiber interwoven or interbraided with a metal fiber can be formed into a one-piece Y-shaped tubular means of the present invention for treatment of abdominal aortic aneurysm with a bifurcated intravascular folded tubular member. Tubular double weaving can be used to reduce leakage sites at crossover points of the metal fibers or strands.
Another embodiment for the abdominal aortic aneurysm intravascular folded tubular member of the present invention has a proximal section with a bifurcated main trunk having an open inlet end and joined to two proximal leg tubes. In this embodiment only one proximal leg tube is joined to a folded section. The other proximal leg tube has an open distal end that is adapted to accommodate a cylindrically shaped intravascular folded tubular member that can be inserted into the open distal end and sealingly engaged with the proximal leg tube using an engagement means positioned on the cylindrically shaped intravascular folded tubular member. This sealing engagement on one side of the proximal section is similar to the modular systems shown for treatment of abdominal aortic aneurysm in the prior art. This embodiment allows one part of the bifurcated intravascular folded tubular member to be unfolded and extended in length in a manner similar to previous embodiments described in this invention, and the other part of the bifurcated intravascular folded tubular member to be extended by adding additional intravascular folded tubular member segments in a modular fashion as described in the prior art.
The folded tubular section for the straight or bifurcated intravascular folded tubular member of the present invention has three layers of intravascular folded tubular member wall that lie in direct contact with or in apposition with each other, an outer wall, a center wall, and an inner wall. These three layers extend from a proximal end to a distal end of the folded tubular section. The length of the folded tubular section becomes shorter as the intravascular folded tubular member becomes extended axially during the deployment of the intravascular folded tubular member. In the folded tubular section a portion of the outer surface of the tubular means is in direct contact with the outer surface of another portion of the tubular means, and a portion of the inner surface is in direct contact with another portion of the inner surface. As the folded tubular section becomes unfolded during the deployment it is desirable for the center wall to not wrinkle during the unfolding process. Such wrinkling can occur if the inner and outer wall slide with respect to the center wall rather than unfolding smoothly from the proximal or distal ends of the folded section. One way of significantly reducing or preventing this wrinkling from occurring is to apply a bonding agent or adhesive to the outside surfaces of the folded tubular section. This adhesive is preferably one that resists the shearing motion that is associated with the relative sliding motion that can cause wrinkles to form. The adhesive should also be capable of undergoing fracture due to exposure to extensional or tension stresses that are generated during the desirable unfolding from the proximal or distal ends of the folded section.
Following deployment of the intravascular folded tubular member of the present invention, it may be desirable to ensure that further unfolding of the folded region does not occur. one or more securing pins or other securing means can be placed through all three walls of the folded tubular section to prevent any further unfolding that may occur after implantation.
The vascular implant of the present invention includes an attachment anchor that can be attached to the inlet or outlet ends of the intravascular tubular member of this invention, the intravascular folded tubular member of this invention, or of any other prior art tubular means used for intravascular implant. The attachment anchor is formed from a metal tube using machining methods that include mechanical, laser, chemical, electrochemical, or other machining methods to form a pattern of nodes and struts. The nodes and struts are intended to provide independent adjustment of expansion force provided by the attachment anchor uniformly outward against the vessel wall due to its expansion deformation and crush elastic force provided by the attachment anchor against external forces that tend to cause the attachment anchor to form an oval shape associated with crush deformation. The independent adjustment of expansion forces due to deformation in the cylindrical surface of the attachment anchor from the crush force which produces a deformation to a smaller radius of curvature in the radial direction of the attachment anchor such as forming an oval shape, allows the attachment anchor of the present invention to have a shorter axial length for a better focal line attachment to the vessel wall.
The nodes are formed of at least one hinge and two transition regions. The transition regions are each attached to a strut. A series of struts and nodes are positioned such that the struts are aligned adjacent to each other forming a single folded ring of struts and nodes with a generally cylindrical shape in a nondeployed state with a smaller nondeployed diameter. The attachment anchor of the present invention can be a balloon-expandable or a self-expanding attachment anchor. During expansion of the balloon-expandable attachment anchor, an expanding means such as a balloon dilitation catheter can be inserted along a central axis of the attachment anchor and expanded. The hinges undergo a plastic expansion deformation as the attachment anchor is expanded to a deployed state with a larger deployed diameter. In a deployed state the hinge exerts an outward expansion force through the struts which in turn push against the blood vessel to hold the vessel outwards and hold the intravascular tubular member against the vessel wall without leakage. A self-expandable attachment anchor is held, for example, within a deployment sheath at a smaller nondeployed diameter for delivery into the vasculature. The hinge is deformed elastically in its nondeployed state and exerts an outward force against the sheath. Upon release from the sheath the self-expandable attachment anchor expands outward until it comes into contact with the vessel wall or the intravascular tubular member. The hinge exerts an outward elastic expansion force through the struts which in turn push against the blood vessel to hold the vessel outwards and hold the intravascular tubular member against the vessel wall without leakage.
Hinges of the present invention have a larger radial dimension than the struts and a thinner width than the struts; the hinge length further having a major role in establishing the outward expansion forces generated by the hinges. The hinge length can be short to focus the expansion deformation of the hinge into a smaller area. For a balloon-expandable attachment anchor the smaller hinge length increases the percentage of metal in the hinge that undergoes a plastic deformation. The result is less rebound of the attachment anchor back towards its nondeployed state following balloon expansion. For a self-expandable attachment anchor the smaller hinge length will generate a greater expansion force for a smaller localized expansion deformation of the hinge. A longer hinge for a self-expandable attachment anchor provides a smaller drop-off of outward expansion force than a smaller hinge length for a specific deployment angle of the attachment anchor. The larger hinge length allows a similar outward force to be applied to the blood vessel wall for a wider range of vessel diameters for the same attachment anchor. For a balloon-expandable attachment anchor an increase in hinge width causes a greater amount of plastic deformation and provides a larger expansion force generated by the hinge than a smaller hinge width. For a self-expandable attachment anchor an increase in hinge width causes a larger outward expansion elastic force to be exerted against the vessel wall. A hinge radial dimension larger than the strut radial dimension produces a larger outward expansion force for both the balloon-expandable or self-expandable attachment anchor. The large hinge radial dimension does not allow the hinge to bend in a radial direction to form an oval such as would like to occur during exposure to a crush deformation.
The struts of the attachment anchor have a larger width than the hinge width such that the hinges can transfer their outward force through the struts to the vessel wall without allowing any bending of the struts in the cylindrical surface of the attachment anchor. The struts have a small radial dimension in comparison to the hinge radial dimension to allow the struts to deform elastically to a smaller radius of curvature in the radial direction of the attachment anchor upon exposure to a crush deformation. The strut width allows the struts to deform elastically at any prescribed crush force during exposure to a crush deformation. A longer strut length allows a greater percentage of the perimeter of the attachment anchor to be associated with the struts in comparison to the hinges or nodes. The longer struts provide the attachment anchor with an increased flexibility in the radial direction when exposed to a crush deformation. Conversely, a shorter strut provides the attachment anchor with a greater stiffness in the crush deformation mode with other attachment anchor dimensions remaining the same. The greater stiffness associated with an attachment anchor with such a shorter length strut allows the strut to be formed with a thinner radial dimension or smaller width and still have the same flexibility in crush deformation as a longer strut.
The attachment anchor of the present invention can be formed out of a higher modulus metal that other attachment devices. Other prior art attachment devices cannot be formed of the highest modulus metal because their expansion force cannot be changed without also affecting their crush force. With the present attachment anchor the outward expansion force can be designed independently from the crush force provided by the attachment anchor. The present attachment anchor can be formed such that it is short in axial length in order to provide a more focused line of attachment to the vessel wall. Short stents formed with prior art designs can be designed to provide an appropriate outward expansion force, however this prior art stent would be too stiff or too flexible in a crush deformation and would be without the ability to adjust the crush deformation force with respect to the outward expansion force. The present attachment anchor can be designed to provide both an appropriate expansion force and an appropriate crush force. The hinge of the present attachment anchor can also provide more expansion force than other prior art attachment devices due to the use of higher modulus metal and due to the dimensions chosen for the hinge width, length, and radial dimension. The close efficient packing of the struts parallel to each other provides the present attachment anchor with a large expansion ratio. The short strut length allows the strut width to be minimized while still maintaining an appropriate flexibility in crush deformation further maximizing the expansion ratio provided by the present attachment anchor. The strong expansion force provided by the hinge allows an appropriate expansion force to be generated such that the attachment anchor of this invention with short axial length can provide adequate expansion forces to hold a large vessel such as the aorta outward and prevent leakage between the intravascular tubular member and the vessel wall.
The vascular tubular member tubular wall structure can be formed from a composite of polymeric and metallic strands that are either woven or braided to provide different characteristics in its axial and circumferential directions. In a weaving process for tubular structures one or more strands have substantially a circumferential direction and another group of strands have generally an axial direction. In a weaving process the substantially circumferential strands generally have a gradual helical wind that is approximately perpendicular to the longitudinal axis of the vascular tubular member but the strands are continuous and actually form a helix. A polymeric strand can be made up of substantially straight filaments to form a straight polymeric strand. This straight polymeric strand can be woven in a circumferential direction forming a straight circumferential polymeric strand, or woven in an axial direction forming a straight axial polymeric strand. The polymeric strand can also undergo a thermal, mechanical, or chemical forming process that can heat set, mechanically set, or chemically deform the polymer filaments or the strand to have local bends, helical spirals, or curves in it. The local bends can be spaced very close together with spacing approximately equal to the diameter of the filament. Alternately, the local bends can be spaced apart further than the diameter of a fiber that is made up of many filaments. This curved polymeric strand will have the characteristic that it can stretch or elongate in its axial direction. This curved polymeric strand can be woven in a circumferential direction forming a curved circumferential polymeric strand, or it can be woven in an axial direction forming a curved axial polymeric strand. The straight or curved polymeric strand could be made from filaments of expanded polytretrafluoroethylene, from filaments of Dacron polyester, polyurethane, or from other suitable polymeric filaments.
The metallic strands that could be interwoven between the polymeric strands could be formed from a straight metallic strands, fibers, or wire formed from a metal such as Nitinol, stainless steel, titanium, tantalum, or other suitable metal or alloy. The wire can be round in cross section or it can be flat wire with a more rectangular cross section. It is preferable for one embodiment that the wire or metallic strand be of an elastic nature that does not exceed its elastic limit during the deployment of the vascular tubular member of the present invention. The wire in another embodiment could undergo plastic deformation during the deployment of the vascular tubular member. This straight metallic strand can be woven in the circumferential direction forming a straight circumferential metallic strand, or it can be woven in the axial direction forming a straight axial metallic strand. The metallic strand can also undergo a thermal, mechanical, or chemical forming process that can heat set, mechanically set, or chemically set the metallic strand to have local bends, helices, or curves in it. This curved metallic strand will have the characteristic that it can either stretch or compress in its overall axial direction. This curved metallic strand can be woven in a circumferential direction forming a curved circumferential metallic strand, or it can be woven in an axial direction forming a curved axial metallic strand. When woven in an axial direction, the curved wire is held under tension and is therefore held in a straight conformation. Upon release of the metallic strand, it forms the curved shape that was formed into the metallic strand prior to weaving. Circumferentially weaving a curved metallic strand requires additional effort due to the tortuous pathway followed by the strand during the weave.
The vascular tubular member wall structure of the present invention can include a woven tubular structure consisting of curved and straight, polymeric and metallic strands in the circumferential and axial directions. In one structure straight circumferential polymeric strands and one or more straight circumferential metallic strands are interwoven circumferentially and straight axial polymeric strands are woven axially. This structure is easy to form and has good hoop strength that will resist kinking due to the metallic component. The folded tubular section has good approximation between the inner, center, and outer walls since only the polymeric strands are extending axially allowing the circumferential fold lines to have a very small radius of curvature.
In another vascular tubular member wall structure additional straight axial metallic strands are interwoven with the straight axial polymeric strands of the structure just presented above. The additional straight axial metallic strands provide the folded tubular section with the characteristic that resists wrinkling in the folded tubular section. A tubular double weave can be used whenever two metal strands form a crossover point. One of the metal strands can be brought out of the plane of the weave prior to the crossover point and reenter the plane of the weave after the crossover point. The weaving plane is thus continuous without one of the metal strands and leakage at that crossover point will not occur. The additional straight axial metallic strands offer axial strength against compressive deformation but can cause the vascular tubular member to become stiff and more difficult to negotiate the tortuous turns of the iliac and femoral arteries.
In still another vascular tubular member wall structure a curved axial metallic strand is interwoven with straight axial polymeric strands in the vascular tubular member wall structure just presented above instead of straight axial metallic strands. The curved axial metallic strands provide a benefit to the folded tubular section to resist wrinkling during the unfolding process. The curved axial metallic strands also provide the vascular tubular member with good axial support against compressive forces generated by the thrombus and other physiological forces that can be placed upon the vascular tubular member. The curved axial metallic strands can compress elastically and thereby will not provide this vascular tubular member wall structure with good flexibility and will resist vascular tubular member kinking.
In yet another vascular tubular member wall structure straight circumferential polymeric strands are interwoven with one or more curved circumferential metallic strands in the circumferential direction and straight axial polymeric strands are interwoven with curved axial metallic strands in the axial direction. The curved circumferential metallic strands found in this structure allows the folded tubular section to unfold with greater ease due to their ability to elongate diametrically as, for example, one curved circumferential metallic strand located in an inner or outer wall passes adjacent to another curved circumferential metallic strand located in the center wall. The curves or bends in the curved circumferential metallic strands also allows the vascular tubular member to expand out uniformly to its deployed diameter which can be smaller than the equilibrium diameter of the vascular tubular member and provide uniform contact with the aortic wall.
In one more vascular tubular member wall structure curved circumferential polymeric strands are interwoven with one or more straight circumferential metallic strands in the circumferential direction and straight axial polymeric strands are interwoven with curved axial metallic strands in the axial direction. The curved circumferential polymeric strands provide an amount of circumferential stretch in the diametric direction. The other components of the weave restrict excessive circumferential stretch. This vascular tubular member structure can also be modified slightly to provide an additional characteristic. Near the proximal end of the tubular means the straight circumferential metallic strands can be eliminated thereby allowing the vascular tubular member to expand to a larger circumference. This circumferential expansion allows the vascular tubular member of the present invention to accommodate a reasonable tolerance in the estimated aortic neck diameter of a few millimeters. Similar circumferential accommodation also applies to the iliac artery.
Accomodation of the estimated aortic diameter with a vascular tubular member of a fixed non-flexible wall material with a maximum diameter can also be accomplished by ensuring that the vascular tubular member chosen can expand to a slightly larger diameter than the aortic diameter. Any embodiment of vascular tubular member wall structure of this disclosure can provide this characteristic. Any excess graft wall material will result in a wrinkle or fold if the perimeter of the tubular member is slightly larger than the perimeter of the aorta, for example. Provided that this wrinkle or fold is held tightly against the aortic wall by the proximal attachment anchor, leakage at the proximal site will not occur.
In yet one more vascular tubular member wall structure curved circumferential polymeric strands are interwoven with one or more curved circumferential metallic strands in one direction and the axial direction is the same as the vascular tubular member wall structure just described above. This structure offers the ability to stretch in the circumferential direction to a limited extent controlled by the amount of curvature provided to the circumferential strands. This vascular tubular member wall structure provides good anti-kink characteristics, good axial support against compression, good flexibility, and will accommodate a reasonable tolerance in the aortic neck diameter, and a tolerance on the iliac artery diameter.
In still one more vascular tubular member wall structure curved circumferential polymeric strands are interwoven with one or more curved circumferential metallic strands in one direction and the axial direction contains curved axial polymeric strands interwoven with curved axial metallic strands. This structure offers the ability to stretch in the circumferential and axial direction to a limited extent controlled by the amount of curvature provided to the circumferential and axial strands, respectively. This structure can extend in each direction throughout the entire tubular means. This vascular tubular member wall structure provides good anti-kink characteristics, good axial support against compression, good flexibility, and will accommodate a reasonable tolerance in the aortic neck diameter, and a tolerance on the iliac artery diameter.
All of the vascular tubular member wall structures presented in this disclosure can be formed with the axial metallic strands being directed with an augmented amount of helical turn. This is accomplished by taking metallic strand out of the weaving plane, stepping over to a new site that is displaced circumferentially, and inserting the metallic strand back into the plane of the weave. This stepping over process allows the axial metallic strand to assume a helical pathway along the axial direction of the vascular tubular member. This augmented amount of helical turn is in addition to the gradual helical turn naturally found in the axially oriented metallic strands due to their natural desire to orient perpendicular to the generally circumferential strands which also have a slight helical turn since they are wound in a continuous helix. The augmented helical turn of the metallic strands in the generally axial direction provides the vascular tubular member with an ability to bend without kinking even when straight metallic strands are used in the axial direction. Enhanced helical turn in the circumferential direction can also be accomplished by weaving two or more metallic strands into the circumferential weave. This can provide a steeper angel for the helical wind and provide additional axial flexibility without kinking.
In a preferred embodiment curved polymeric strands are wound in both the circumferential and axial direction to provide the vascular tubular member with a supple feel and good bending characteristics without kinking. For simplicity of manufacturing, one or more straight metallic strands are wound in the circumferential direction. Either curved metallic strands or straight metallic strands with the step over characteristic described above is used in the axial direction to provide the necessary compressive strength as well as provide good flexibility to the vascular tubular member. An entire straight or bifurcated vascular tubular member can be formed from a single contiguous woven material comprised of the polymeric and metallic strands described above. The vascular tubular member is woven without seam in its proximal, folded or distal section. For the bifurcated tubular member this is accomplished by splitting the number of strands that extend axially such that approximately half of those present in the main trunk extend down one proximal leg and half extend down the other proximal leg.
The vascular tubular member wall structure of the present invention can also be formed from a braiding process wherein straight polymeric and straight metallic strands are braided in a right hand spiral forming straight right spiral polymeric strands and straight right spiral metallic strands. These strands can be made with localized bends or curves in them as described earlier, and these strands can be braided into a right hand spiral to form curved right spiral polymeric strands and curved right spiral metallic strands. Similarly the straight and curved, polymeric and metallic strands can be braided into a left hand spiral.
In one vascular tubular member wall braided structure a straight right spiral polymeric strand and a straight right spiral metallic strand are interbraided together in one direction and a straight left spiral polymeric strand and a straight left spiral metallic strand are interbraided in the opposite direction. The braiding process provides some ability for this wall structure to accommodate reasonable tolerances in the estimation of the proximal aortic neck diameter in order to provide a good diametric fit between the vascular tubular member and the proximal aortic neck. The presence of the straight and curved metallic strands provides good axial and circumferential strength and stability against compression in the radial or axial direction in comparison to other prior art materials of construction.
In other vascular tubular member embodiments the braided structure can involve either curved metallic strands or curved polymeric strands. These curved metallic or polymeric strands will provide the vascular tubular member with a greater flexibility due to the ability of these metallic strands to compress as the vascular tubular member is exposed to a tortuous pathway.
It is understood that the woven and braided vascular tubular member wall structures presented are not intended to be complete and that other combinations of straight and curved, polymeric and metallic strands can be used with weaving or braiding with the associated characteristics and advantages that have been described or taught in this disclosure.
The bifurcated tubular member used in the treatment of abdominal aortic aneurysm described in this invention can have a proximal attachment anchor attached at the proximal end of the bifurcated main trunk. This attachment anchor provides a circumferential expansion and attachment to the aorta without significant change in axial length. This small axial length change allows this attachment anchor to be placed very near to the renal arteries with precision and reduce the likelihood for distal migration of the vascular tubular member. A greater number of barbs can be placed on the attachment anchor due to the geometry of the attachment anchor which has a short axial length and involves a hinge to supply the outward forces of the attachment anchor. The increased number of barbs will better hold the vascular tubular member to the aorta around the entire circumference.
The bifurcated folded tubular member of the present invention can also have a proximal attachment anchor that is displaced proximally from the proximal end of the main trunk. The displaced attachment anchor can be joined to the bifurcated main trunk by the metal strands that are woven axially or helically into the vascular tubular member or by the metal strands that are braided into the vascular tubular member. The displaced proximal attachment anchor is intended in one embodiment to provide attachment proximal to the renal arteries in a region of the aorta that is significantly proximal to the aneurysmal region of the aorta. Since many abdominal aortic aneurysms occur adjacent to the renal vessels and generally distal to the renal vessels, it is sometimes necessary to find a proximal attachment site that is proximal to the renal arteries. The displaced proximal attachment anchor will provide this attachment capability and prevent any distal migration of the intravascular tubular member. The small metallic strands that connect the displaced attachment anchor to the main trunk of the intravascular tubular member can cross over a renal artery without causing a significant thrombotic or occlusive effect. The metallic strands are positioned around the circumference to provide the main trunk with support from the attachment anchor along its entire circumference. Only a minimal number of metallic strands extend to the displaced attachment anchor in order to reduce the chances for thrombus formation at the entrances to the renal arteries. The number of strands can range from two to approximately sixteen. An additional proximal attachment anchor may be attached to the open proximal end of the main trunk in addition to the displaced attachment anchor to provide a tight leak-free seal with the aorta. The displaced attachment anchor can have barbs to enhance attachment to the aorta or it can be an attachment anchor without barbs as described earlier. The metallic strands can be attached to selected securing sites of the attachment anchor.